Modular gearbox for a variable pitch fan propulsor

ABSTRACT

For a ducted fan propulsor a modular speed reduction gearbox driven by a turbine type of power plant is disposed fore of the plane of rotation of the variable pitch fan relative to the forward direction of the vehicle driven by the power plant.

United States Patent [191 Andrews et a1.

1 Sept. 2, 1975 MODULAR GEARBOX FOR A VARIABLE PITCH FAN PROPULSOR [75]Inventors: Merritt B. Andrews, Westfield,

Mass; Thomas F. McDonough, Windsor, Conn.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

22 Filed: Feb. 21, 1973 21 App1.No.:334,350

[52] US. Cl 416/170; 416/160 [51] Int. Cl B63h 3/02 [58] Field of Search416/160, 152, 170; 74/640 [56] References Cited UNITED STATES PATENTS1,481,024 l/1924 Porter 416/170 1,856,529 5/1932 Zerbi 416/170 1,967,7537/1934 Houston 416/170 2,001,736 5/1935 Larason 1. 416/170 2,648,3878/1953 Doman 416/160 X 3,314,310 4/1967 Quennevi11e.... 74/801 3,647,3203/1972 Chilman et a1. 1. 416/160 X FOREIGN PATENTS OR APPLICATIONS496,824 12/1938 United Kingdom 416/ 160 Primary ExaminerEverette A.Powell, Jr. Attorney, Agent, or F irmNorman Friedland 5 7 ABSTRACT For aducted fan propulsor a modular speed reduction gearbox driven by aturbine type of power plant is disposed fore of the plane of rotation ofthe variable pitch fan relative to the forward direction of the vehicledriven by the power plant.

4 Claims, 9 Drawing Figures MODULAR GEARBOX FOR A VARIABLE PITCH FANPROPULSOR BACKGROUND OF THE INVENTION This invention relates to variablepitch ducted fan propulsors and particularly to the gearbox andconstruction thereof.

As is well known in the propeller art the gearbox is conventionallymounted fore of the engine behind the propeller. The gearbox serves totransmit torque from the engine power shaft to the propeller at a givenreduced speed. In variable pitch ducted fans of the type exemplified inUS. Pat. No. 3,489,338 granted to .I. A. Chilman on Jan. 13, 1970 asimilar type of concept for gear reduction has been employed, typifyingwell established design principles in the propulsor field.

The purpose of this invention is to construct the reduction gearbox sothat it is mounted ahead of the pitch change mechanism and the plane ofrotation of the rotor and in doing so the following features areobtained:

l. The accessibility of the gearbox for maintenance and conditionmonitoring is facilitated.

2. The necessity of having to pass the pitch change input signal throughor around the gear reduction stage is eliminated, since it is directlyconnected to the blades.

3. The need to compromise the engine inlet duct de sign is obviatedsince it isnt necessary to duct around a gear reducer.

4. Lubricating oil can be removed from the blade disk retention area byutilizing the gear reduction scavenger system.

5. Makes available ample length to permit a working quill between thegas generator and gearing on a closely coupled fan turbine system.

6. Allows for a more optimum rotor support system by keeping the aftportion of the rotor disk free of gear- 7. Provides a minimum ofenvelope restriction for the most optimum gear sizing.

SUMMARY OF THE INVENTION It is an object of this invention to providefor a variable pitch ducted fan type of propulsor an improved gearbox.

A still further object of this invention is to provide for a variablepitch ducted fan propulsor gearbox means mounted forward of the plane ofrotation of the fan rotor as viewed with respect to the forwarddirection of the vehicle.

A still further object of this invention is to provide for a variablepitch fan propulsor driven by turbine type of power plant, a modulartype of planetary gear train disposed forward of the plane of rotationof the fan rotor.

Other features and advantages will be apparent from the specificationand claims and from the accompanying drawings which illustrate anembodiment of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view partly inelevation, partly in section illustrating a variable pitch ducted fanpropulsor.

FIG. 2 is a partial view partly in section and partly in side elevationshowing the details of this invention.

FIG. 3 is a sectional view taken along line 33 of FIG. 2..

FIG. 4 is a perspective cut-away view partly in section illustrating apitch change system.

FIG. 5 is a sectional view illustrating a no-back actuator.

FIG. 6 is a sectional view taken along the lines 66 of FIG. 5.

FIG. 7 is a diagrammatic view illustrating the operation of the no-backshown in FIG. 5.

FIG. 8 is a showing of FIG. 7 in increase pitch condition.

FIG. 9 is a showing of FIG. 7 in a decrease pitch condition.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 the variablepitch ducted fan propulsor is generally illustrated by numeral 10comprising a turbine type of power plant illustrated by numeral 12 shownin blank driving the fan 14 housed within the duct 16 supported theretoby a plurality of stator vanes 18. The fan may include spinner 20 whichserves to provide a smooth aerodynamic surface for directing the airflowthrough the fan, where a portion is discharged through the outlet ofduct 16 via the stator vanes and a portion is directed into the inlet 24of the engine 12. Such variable pitch ducted fan propulsors arecurrently being developed by the Hamilton Standard Division of UnitedAircraft Corporation and while this invention is described in itspreferred embodiment as being directed for aircraft propulsors it is tobe understood as will be obvious to one skilled in the art that thisinvention may have applications for other embodiments.

The details of this invention may best be seen by referring to FIG. 2which shows the hub 26 supporting the blades 15 (one being shown)circumferentially spaced about axis 64 driven by the power shaft 28through the planetary gearing system illustrated by numeral 30. Thepitch change actuating system comprises the input actuator 32, thedifferential 34 and the harmonic drive 36 all of which will be describedhereinbelow.

The power shaft 28 driven by the engine 12 is splined to the sun gear 38driving a plurality of planetary gears 40 which in turn are in mesh withthe ring gear 42. Each of the plurality of planet gears rotatablysupported to the spoke 44 are interconnected by a pair of straps 46 and48 attached on either end. The operation and details of a suitableplanetary gearing system is described and claimed in US. Pat. No.3,314,310 granted to Raymond N. Quenneville on Apr. 18, 1967 andassigned to the same assignee and is incorporated herein by reference.

As is apparent from the foregoing, the power taken off of the powershaft 28 is transmitted to the ring gear 42 at a reduced speed andtransmitted to the hub via connection 50 which carries a pair of flanges52 and 54 attached to the hub 26 by a plurality of nut and boltassemblies generally illustrated by 58 and ring gear 42 by a pluralityof nut and bolt assemblies 60. Connection 50 is annular shaped and madefrom suitable material such that it is capable of being locallydeflected radially, while being stiff in the torsional and transverseshear directions. This construction serves to isolate the deflections ofthe fan from the ring gear 42. Member 51, also annularly shaped, islikewise bolted to the flange 54, and its stiffness characteristics arematched to the stiffness characteristics of connection which preventsany out of plane distortion on ring gear 42. The hub 26 is suitablysupported for rotary movement by bearings and 62 so as to be rotatableabout axis 64. The support housing 66 supporting bearings 60 and 62extends inwardly and also supports the spokes 44 (only one of which isshown) of the planetary gears.

As will be fully described hereinbelow the blades 15 of the fan arerotatably supported to the rotor hub 26 for pitch change movement. Eachblade carries a segment gear 68 formed on stub shaft 69 suitablyconnected to the root of the blades, as in this instance by spline 70and is rotatably supported therein by bearing 71. It being understoodthat the segment gear can be made integral with the blade root. Eachblade is rotatably supported within the hub 26 by its own bearing 72 andsupported by the retention mechanism 74. The shielded bearing 71 permitsremoval of individual blades without exposing the rotor and gearboxcavity.

Pitch change actuation is accomplished through the harmonic drive 36which is interconnected to segment gear 68 and differential gear train34. To effectuate pitch change movement the input rotary shaft 76 whichin turn is controlled by a suitable control transmits the pitch changeinput signal to differential gear train 34 via the one-way drive 32. Itshould be understood that the one-way drive can be located on eitherside of the differential.

Consider for the moment that the control calls for a change in pitch ofthe fan blades, the control (not shown) serves to drive the input shaft76 by rotating it clockwise or counterclockwise to rotate gear 78through the oneway drive 32. This will impose a rotary signal to thedifferential. The differential is composed of a grounded sun gear 80,input sun gear 82, two groups of three planet gears 84 and 86 (only oneof each group being shown) supported to a common carrier 88, a referencespeed ring gear 90 and a second output ring gear 92 connected to theharmonic drive 36. As can be seen from FIG. 2 the reference speed ringgear 90 is suitably splined by spline 91 to the hub 26 so that itrotates therewith. A grounded sun gear is likewise splined to theannular portion 94 of the spoke element 44 by spline 96. Annular portion94 is splined to the fixed housing 66 so that sun gear 80 can beconsidered as a grounded or fixed member. With no pitch change inputsignal the speed of the carrier 88 is established by the reference speedring gear and the grounded sun gear 80. The application of a pitchchange signal by virtue of rotation of gear 78 will cause sun gear 82 torotate causing the planet carrier 88 to rotate to advance or retard ofthe established speed set up when there was no pitch change input signalcondition. This retardation or advancement of the carrier produces arelative rotation between the reference and output ring gears. Thisrotation differential is the input to the harmonic drive 36.

The harmonic drive which is a high-ratio, speed reduetion device iscomprised of three basic components: lobed wave generator 100, flexingmember or flexspline 102 and rigid circular ring or rigid spline 104.The wave generator is composed of a thin race ball bearing deflected inan ellipsoidal shape by the similar shaped rotating rigid disk withinit. Flexspline 102 which is a thin wall cylinder and deflected intoellipsoidal cross section by the wave generator imparts rotary motion tothe circular spline 104 which carries mating teeth 106 engaging teeth 68of the segment gear for rotating the blade 15 about its longitudinalaxis for changing its pitch. The pitch in this instance may include,positive, negative, reverse and feather, and the movement may includegoing from positive thru reverse to feather or from positive to featherand to reverse, or any combination thereof. A suitable harmonic drive isdisclosed in U.S. Pat. No. 2,906,143 to C. S. Musser dated Sept. 29,1969 and said patent is incorporated herein by reference.

The operation of a harmonic drive can probably best be understood byreferring to FIG. 3 which shows a rigid circular ring 104 havinginternal teeth 108 engaging with the external teeth 110 of theflexspline 102. The thin race 112 of the wave generator when rotateddeflects into an ellipsoidal shape by virtue of the rotating rigid disk114 disposed adjacent to balls 1 16 of the ball bearing. The teeth atthe major axes (dash line 118) are always in mesh and the teeth at theminor axes (dash line 120) are out of mesh. Since there are fewer teethon the flexspline then on the circular rigid ring, each rotation of thewave generator moves the flexspline to a distance equal to the toothdifferential between the splines.

As the wave generator is rotated it'causes progessive tooth engagement.This causes rotation of the circular spline which carries teeth 106which engages the segment gear 68 for imparting rotational movement(pitch change) to each individual blade. It is to be understood thateach blade carries a similar segment gear which also is in contact withteeth 106 of the rigid circular ring.

The operation of the harmonic drive and the differential gear train canprobably best be appreciated by referring to FIG. 4 that shows thedetails in schematic and in perspective. It will be appreciated that thedifferential gear train is used as the interface between the rotatingand stationary components of the fan so that the pitch or blade anglepositions are capable of being transmitted across a rotating boundary.Looking at the differential gear train it will be appreciated that inthis embodiment the sun gear 206 is affixed or made integral with fixedshaft 204 of the differential and engages a plurality of (three)planetary gears 208 These planetary gears, in turn, engage ring gear 210which is carried by or affixed to rigid disc 212 of the harmonic drive.Shaft 214 concentric to shaft 204 but rotatably disposed relativethereto carries spur gear 218 which is in mesh with the pitch changinginput mechanism 220 and pinion gear 222. Mechanism 220 is a one-wayclutch that responds to the pitch control signal and will be describedin more detail hereinbelow. Sun gear 224 affixed to or made integralwith shaft 214 engages a plurality (three) of planetary gears 226 andeach planetary gear 226 in turn engages the internal gear or ring gear228 formed on the rotor 230 which supports blades 232. The rotor, itbeing noted, is driven by shaft 234 which in turn is driven by theengine (not shown). Planetary gears 208 and 226 are carried by thecarrier 236 supporting stub shafts 240.

It is apparent from the foregoing that sun gear 206 is held fixed sinceit is grounded to shaft 204 and that the planetary gears 226 driven bythe reference speed ring gear 228 establishes the speed of carrier 236.The addition of a signal for either an increase or decrease pitch changemovement will cause pinion gear 222 to rotate sun gears 224 via gear 218and shaft 214 causingcarrier 236 to either advance or retard from itsestablished speed. This advancement or retardation, in. turn, changesthe speed of ring gear 210 relativelto the rotor hub 230 and henceserves as the input to the harmonic drive. That is to say, it causes thewave generator disk 212 to either rotate clockwise orcounterclockwiscdepending upon whether it was an'advancement orretardation caused by the pitch change input signal.

As was described above the differential gear train transmits a pitchchange signal across a rotating boundary and becomes the input to theharmonic drive. The next portion of the description will deal with theharmonic drive. g l l As mentioned earlier the harmonic drive consistsof the wave generator, flexspline and a rigid circular ring or circularspline.

The wave generator consists of rigid disk 212 forming one race of theball bearing and caused to rotate by ring gear 210. The other race 251which is a thin'flexible circular wall, deflects into an ellipsoidalshape by virtue of the similarly shaped rotating rigid disk within it.

Flexing element or flexspline 250 is in the form of a thin walledflexible cylinder, is deflected on one end adjacent the balls 253 of theball bearing into the ellipsoidal cross-sectional shape. The other endof the cylinder is supported by or secured to the rotor and is held incircular cross section. By virtue of the ellip-soidal shape of the rigiddisk 212 which is transmitted to the flexspline and the differential inthe member of teeth 252 formed integral with or affixed to the circularspline 256, the circular spline will move at a reduced speed from thatof the input. Extremely high ratios of speed reduction are manifested bythis mechanism with a consequential transmission of large torque.

Since the teeth of gear 260 affixed to the circular spline, rotatablysupported by balls 261 to the rotor 230 for relative movementtherebetween, meshes with segment gear 262 formed on the root of blade232 it is apparent that the blade will rotate about its longitudinalaxis and hence change blade angle (pitch).

If it is desirable to prevent the pitch of the blades to advance beyonda preascertained blade angle suitable stops may be employed. In thisinstance lug 270 affixed to and extending from the face of circularspline is made to abut against lug 272 extending downwardly from rotorhub 230. Obviously, since lug 272 is fixed and lug 270 rotates and sincecircular spline varies blade angle, by indexing the blade angle to therelative position of the lugs, the contact point will determine thebarrier between the point where blade angle is and is not adjustable.Thus barrier lug can be used to limit low and high pitch extremes. Inlike manner intermediate removable stops can be executed.

As was mentioned above the one-way clutch 32 of FIG. 2 and the one-wayclutch 220 of FIG. 4 serve to transmit the control signal from the pitchchange control (not shown) to the differential. This effectively rotatesgear 78 of FIG. 2 and gear 222 of FIG. 4 clockwise or counterclockwisein response to the polarity and magnitude of the input thereto. Thecircular spline in both schemes are correspondingly rotated in aclockwise or counterclockwise direction for effectuating pitch changingmovement and this movement is generally referred to as raising orlowering the load. The purpose of the one-way drive is to precludeunscheduled blade excursions to either increase or decrease pitch'in theevent of the lossv of the command signal (rotation of input shaft 76 bythe control system not shown). This unitoperates on the principle of aself-energizing brake. Blade twistingtorques when not supported by theinput shaft 76 are grounded to the one-way drive case, locking theblades in the last setposition. This effectively achieves pitch lockingwithout the attendant complicated pitch locking mechanism of theconventional heretofore known designs. r 1

A suitable one-way drive, such as the one capable of use in the FIG. 2and FIG. 4 embodiments is illustrated in FIGS. 5-9. The inner wall ofbore 300 of casing 302 serves as a grounded braking hub by the actionand reaction of the coil spring 304. The spring is interference fittedinto the bore'and normally engages wall of bore 300. The input shaft 306may be splined to the spring actuator connector 310 via spline 308,splines 3 12, 314 and 334 by extending through output spline segment329. Splines 312 and 314 are adapted to engage tangs 316 and 318 onopposite ends of coil spring 304. This serves to drive the spring endsin a predetermined phase with the input. Output shaft 326 supported incasing 302 by suitable bearings 320, 322 and 324 is rotated clockwise orcounterclockwise depending on whether the input signal calls forincrease or decrease pitch through an interrupted spline 334 and spline330. The spline connection 328 and 329 interconnects the output shaft326 via splines 330, 328, 331 and 318 to the coil spring 304. Throughproper phasing of the aforementioned splining a command input signal canrelease the spring from the case ground and continue to drive throughthe device to rotate the output. However, the output shaft is incapableof completing spring release, but further expands the spring into thecase causing the self-energizing brake effect.

The operation phasing of the one-way drive can probably best beunderstood by referring to the opera tional diagrams shown in FIGS. 7, 8and 9. Additional description of the one-way drive may be had byreferring to US. Pat. No. 3,631,951 granted to R. N.

Ouenneville on Jan. 4, 1972 and assigned to the same assignee. Heretangs have been used to diagrammatically illustrate the splines and thespring has been illustrated as having only one coil (the prime referencenumerals as used herein are diagrammatic showings of the elementsreferenced by its like unprimed numerals). Rotation of the load shaft326 in either direction drives the spring into an increasing furled fitwith the grounded housing 300 and friction locks these members, henceachieving pitch lock (at this time the input drive 314, 312 does notengage the spring).

Decreasing pitch diagrammatically illustrated in FIG. 9 shows the inputengaging the tang of the coil spring to unwind it from the hub andpermitting the rotational movement.

Increase pitch shown in FIG. 8 shows the input engaging the tang of thecoil. This drags the spring within the housing allowing rotation of theoutput shaft.

It should be understood that the invention is not limited to theparticular embodiments shown and described herein, but that variouschanges and modifications may be made without departing from the spiritor scope of this novel concept as defined by the following claims.

We claim:

1. A ducted fan propulsor driven by a turbine type of power plant, arotatable hub supporting a plurality of circumferentially spaced blades,21 fixed hollow support sleeve having bearing means, a hollow sleeveportion of said hub extending rearwardly relative to said bladessupported by said bearing means within a cavity defined by said hollowfixed sleeve, a planetary gear train including planet support meanssupported to said fixed support means forward of said hub, a ring gearand sun gear, means including a relatively thin annularly shaped memberinterconnecting said hub and said ring gear for transmitting motion forrotating said hub, a concentrically mounted shaft extending through anannular centrally located space adjacent the rotating axis defined bysaid hollow fixed sleeve interconnecting said turbine type power plantand said sun gear, and a plurality of planet gears rotatably supportedto said planet support means for transmitting torque imparted to saidsun gear by said turbine type power plant driven shaft to said ring gearfor driving said hub.

2. A ducted fan propulsor as claimed in claim 1 wherein said relativelythin annularly shaped member has a flange clement secured to said hub inproximity to the roots of said blades and said member being cap-u. bleof being locally deflected radially and being stiff in a torsional andtransverse shear direction.

3. A ducted fan propulsor as claimed in claim 2 including anotherrelatively thin annularly-shaped element supporting said ring gear andattached to one end of said annularly shaped member also characterizedas being capable of being locally deflected radially and being stiff ina torsional and transverse shear direction whereby out-of-planedistortions on said ring gear are substantially minimized.

4. A ducted fan as claimed in claim 1 including pitch change meanshaving rotary pitch change means rotatably supported to said fixedsleeve centrally of said hub including a gear train connecting the rootof said blades, an actuator fixed to said fixed hollow sleeve includinga rotating drive gear for imparting pitch change motion to said geartrain for effectuating pitch change movement to said blade, and acontrol shaft extending through said fixed hollow sleeve for controllingmovement of said gear.

1. A ducted fan propulsor driven by a turbine type of power plant, arotatable hub supporting a plurality of circumferentially spaced blades,a fixed hollow support sleeve having bearing means, a hollow sleeveportion of said hub extending rearwardly relative to said bladessupported by said bearing means within a cavity defined by said hollowfixed sleeve, a planetary gear train including planet support meanssupported to said fixed support means forward of said hub, a ring gearand sun gear, means including a relatively thin annularly shaped memberinterconnecting said hub and said ring gear for transmitting motion forrotating said hub, a concentrically mounted shaft extending through anannular centrally located space adjacent the rotating axis defined bysaid hollow fixed sleeve interconnecting said turbine type power plantand said sun gear, and a plurality of planet gears rotatably supportedto said planet support means for transmitting torque imparted to saidsun gear by said turbine type power plant driven shaft to said ring gearfor driving said hub.
 2. A ducted fan propulsor as claimed in claim 1wherein said relatively thin annularly shaped member has a flangeelement secured to said hub in proximity to the roots of said blades andsaid member being capable of being locally deflected radially and beingstiff in a torsional and transverse shear direction.
 3. A ducted fanpropulsor as claimed in claim 2 including another relatively thinannularly-shaped element supporting said ring gear and attached to oneend of said annularly shaped member also characterized as being capableof being locally deflected radially and being stiff in a torsional andtransverse shear direction whereby out-of-plane distortions on said ringgear are substantially minimized.
 4. A ducted fan as claimed in claim 1including pitch change means having rotary pitch change means rotatablysupported to said fixed sleeve centrally of said hub including a geartrain connecting the root of said blades, an actuator fixed to saidfixed hollow sleeve including a rotating drive gear for imparting pitchchange motion to said gear train for effectuating pitch change movementto said blade, and a control shaft extending through said fixed hollowsleeve for controlling movement of said gear.